1. Technical Field
This application relates generally to liquid crystal display technology, and more specifically to volume stabilized ferroelectric liquid crystal materials, and display cells produced therewith.
2. Description of the Prior Art
Ferroelectric liquid crystal cells suitable for liquid crystal electro-optic switching devices have been shown to have numerous advantages over cells employing nematic liquid crystals due to the advantageous physical properties of ferroelectric liquid crystals. Ferroelectric liquid crystals exhibit faster switching times and an excellent memory effect due to their pronounced structural bistability. Switching of ferroelectric liquid crystals is simplified because they require only a passive thin-film electrode control matrix which, unlike the active matrices required by nematic liquid crystals cells, does not consist of transistors and diodes.
In Appl. Phys. Lett. 36, 11 (1980) and in U.S. Pat. No. 4,367,924, N. A. Clark and S. T. Lagerwall described a surface stabilized ferroelectric liquid crystal cell. The arrangement of liquid crystal molecules is accomplished by means of a surface alignment layer being provided on either bounding plate of the cell. The distance between the bounding plates is controlled by spacers, such as glass fibers, particles of a granulated material, polystyrene spherical microparticles and the like, which are distributed throughout the cell. In spite of subsequent improvements, as reported in, for example, U.S. Pat. No. 4,958,916; Ferroelectrics 59, 25 (1984); Molecular Crystals and Liquid Crystals 114, 151 (1984) and Phys. Rev. A 37,3 1053 (1988), ferroelectric liquid crystal cells are particularly sensitive to mechanical disturbances. Moreover, since it is difficult to stabilize the distance between the bounding plates, currents of the liquid crystal arise within the cell and destroy the original arrangement of the ferroelectric liquid crystal. Similarly, if the cell is subjected to a substantial temperature increase the arrangement of the liquid crystal is destroyed and, by themselves, the surface alignment layers may be ineffective to restore the original arrangement unless special thermal procedures are used.
The use of composite materials, such as a liquid crystal within a polymer, is also known as seen, for example, in Liquid Crystals, Vol. 4, pp 327-336 (1986), and U.S. Pat. Nos. 4,688,900, 4,685,711 and 4,994,204. However, substantial amounts of a polymer are required for these cells to obtain microdroplets of liquid crystal within the polymer. The liquid crystal molecules in the microdroplets are oriented radially or bipolarly. By an electric field between the bounding plates of the cell, light scattering in the composite material is controlled.